The electro-photographic method is ordinarily a method in which an electrostatic latent image carrier consisting of a photo-conductive light-sensitive material is charged, an electrostatic latent image is formed by exposure to light, this electrostatic latent image is then developed by means of a toner composition in which a coloring agent is contained in a bonding resin, and the toner image thus obtained is then transferred to a support such as a transfer paper and fixed so that a visible image is formed. Generally, toner compositions in which a black coloring agent such as carbon black is dispersed in a bonding resin are widely used as toner compositions for obtaining such visible images. In recent years, however, methods in which color images are formed by successively repeating development using colored toners such as cyan, magenta and yellow toners, transferring [the resulting toner image] onto paper and fixing this image have also been used.
In the cases of color transfer images obtained by such methods, images that are close to natural colors are generally required. Accordingly, the vividness, transparency, luster and gradation characteristics of the colors in the respective monochromatic toners have an effect. Color reproducibility is obtained by subtraction color mixing using toners of the three basic colors of yellow, magenta and cyan, and it is necessary to use transparent toners that transmit light. In the case of images in which transparent films are fixed as well, color reproducibility is impossible unless the transparency is good.
Conventionally, copper phthalocyanine pigments (U.S. Pat. No. 3,998,747), copper phthalocyaninesulfonic acid derivatives (Japanese Patent Application Kokai No. S56-57042), β-type copper phthalocyanine pigments (Japanese Patent Application Kokai No. S62-255956), and copper phthalocyanine phthalimide methyl derivatives (Japanese Patent No. H2-135459), etc., have been known as coloring agents used for cyan in electrostatic charge developing toners. Furthermore, a method in which fine particles of silicon oxide are added to organic pigments in order to improve the transparency of the toner is also known (Japanese Patent Application Kokai No. H11-7157).
However, cyan toners of the above-mentioned prior art have an insufficient transparency in terms of requirements that have arisen in recent years, and color reproducibility sufficient for use in full color applications cannot be obtained in the case of such toners.
Furthermore, cyan toners of the above-mentioned prior art are used in mixtures with carrier particles such as ferrites, etc. As a result, the balance with the carrier particles breaks down in the developing process so that differences in the shade of the color are generated; as a result, there are problems in color reproducibility in full color applications.
The object of the present invention is to provide an electrostatic charge developing toner with superior color reproducibility [i] which has sufficient transparency for use as a cyan developing agent, and [ii] which exhibits a vivid green color in the case of superimposition with a yellow developing agent, a vivid blue color in the case of superimposition with a magenta developing agent, and a vivid black color in the case of superimposition with yellow and magenta developing agents.
In light of the above facts, the present inventors conducted diligent research in order to eliminate the drawbacks of the prior art. As a result of this research, the inventors succeeded in perfecting the present invention. Specifically, to solve the above-mentioned problems, the present invention provides an electrostatic charge developing toner which is characterized by the fact that in an electrostatic charge developing toner which uses a bonding resin and a coloring agent as essential components, a β-type copper phthalocyanine pigment which has a BET specific surface area of 90 m2/g or greater is used as the coloring agent.